From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [RFC] CPUID usage for interaction between Hypervisors and	Linux.
Date: Wed, 01 Oct 2008 16:34:09 -0500
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Cc: akataria@vmware.com, "avi@redhat.com" <avi@redhat.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	Gerd Hoffmann <kraxel@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@elte.hu>,
	the arch/x86 maintainers <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	Daniel Hecht <dhecht@vmware.com>,
	Zach Amsden <zach@vmware.com>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
To: Jeremy Fitzhardinge <jeremy@goop.org>
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Jeremy Fitzhardinge wrote:
> Alok Kataria wrote:
>
> I guess, but the bulk of the uses of this stuff are going to be 
> hypervisor-specific.  You're hard-pressed to come up with any other 
> generic uses beyond tsc.

And arguably, storing TSC frequency in CPUID is a terrible interface 
because the TSC frequency can change any time a guest is entered.  It 
really should be a shared memory area so that a guest doesn't have to 
vmexit to read it (like it is with the Xen/KVM paravirt clock).

Regards,

Anthony Liguori

>   In general, if a hypervisor is going to put something in a special 
> cpuid leaf, its because there's no other good way to represent it.  
> Generic things are generally going to appear as an emulated piece of 
> the virtualized platform, in ACPI, DMI, a hardware-defined cpuid leaf, 
> etc...